Crucial Time Nears on Iran Nuclear Talks

Like Iran's nuclear program itself, the international effort to stop it is about to enter a critical phase. Put simply, it now seems possible that the world will know by the end of April whether diplomacy will be sufficient to halt what some fear is an Iranian march toward nuclear-weapons capability.

Iran continues to enrich uranium at two facilities, and it is working on a separate heavy-water reactor that would be able to produce...